In recent years, a service using AR (Augmented Reality) technology has been developed and provided. For example, a technique that acquires an object placed in the vicinity of the located position of a mobile terminal and displays an object including various information and images superimposed on an image acquired by a camera included in the mobile terminal is known. In this technique, an object to be superimposed is selected based on the located position of the mobile terminal. Further, the mobile terminal displays an object based on a positional relationship between the located position of the terminal itself and the position of the object. It is thus important in this technique to accurately detect the located position of the mobile terminal. For example, a technique that acquires the position of an arbitrary landmark object captured by a camera included in a terminal device from a database that pre-stores the positional information of landmark objects and calculates the position of the terminal device based on the acquired position of the landmark object is known (for example, see Patent Literature 1).